The present invention relates to, for example, a fuel quality determining method, a program, a computer readable recording medium which stores the program, and a fuel quality determination device which is used for inspecting quality of fuel (fuel oil) such as heavy oil used in a marine diesel engine.
Conventionally, as fuel for a marine diesel engine (diesel fuel) used mainly in foreign-bound ships, heavy oil is used. Heavy fuel contains a high rate of residue oil produced along with refining of crude oil. Such marine diesel fuel is also referred to as bunker oil.
Bunker oil contains a high rate of residue oil as described above and hence, components of bunker oil differs depending on a method for refining crude oil, a production site or the like and therefore quality of bunker oil is not uniform. Accordingly, a foreign-bound ship which refuels (fuel oil) by stopping at ports of countries other than ports of her own country receives refilling of fuel which differs in quality according to country since a crude oil refining method or the like differs from country to country. Further, depending on a country, there may be a case where a foreign-bound ship refuel with very poor quality fuel. Particularly, with the development of a technique for producing gasoline or the like from bunker oil by refining recent years, there has been observed a tendency where quality of bunker oil is lowered attributed to the extraction of gasoline from bunker oil.
Refueling with very poor quality fuel causes troubles relating to an engine. Particularly with respect to a marine diesel engine, scuffing is named as one of most serious troubles. Scuffing is a phenomenon where a piston (piston ring) slides relative to a cylinder (cylinder liner) in a state where a lubricant is in short supply in the engine so that a damage such as flaws and cracks occurs on a wall surface of the cylinder, and this scuffing may cause malfunction of the engine depending on the degree of the damage.
The mechanism that scuffing occurs is complicated, and the design of an engine, heat resistance of lubrication oil, an operation state of the engine, defective maintenance or the like is considered as a cause of the occurrence of scuffing. One of main causes of occurrence of scuffing is quality of fuel. To be more specific, when fuel has good quality, fuel injected into a combustion chamber of an engine is burnt out and disappears instantaneously after the injection of fuel is finished and hence, there is no possibility that the seizure of lubrication oil occurs between a piston and a cylinder. To the contrary, when fuel has vary poor quality, a flame of high temperature which is generated by fuel injected into a combustion chamber remains in the vicinity of a wall surface of a cylinder after the injection of fuel is finished and hence, the seizure of lubrication oil occurs between a piston and a cylinder thus giving rise to scuffing. In this manner, scuffing occurs due to worsening of lubrication property in an engine.
When quality of fuel to be supplied to an engine can be inspected in advance, the above-mentioned engine trouble can be obviated. With respect to the quality of fuel, ignitability is extremely important in the case of diesel fuel. This is because in the case where the fuel is not ignited, the combustion does not start. However, with respect to bunker oil (heavy oil), even when the combustion starts once, there may be a case where combustibility in succeeding combustion is bad. This drawback is brought about by a fact that bunker oil contains residue oil at a high rate as described above and a fact that the lowering of quality of bunker oil caused by the extraction of gasoline from bunker oil progresses.
To be more specific, a residue which is a product produced when gasoline is extracted from heavy oil has so high viscosity that the residue cannot be used as fuel. However, by mixing a byproduct which is produced along with the refining of gasoline from heavy oil into the residue, the adjustment of viscosity of the residue becomes possible. Here, the byproduct means an oil component which has low viscosity and exhibits poor ignitability and poor combustibility such as light cycle oil. Accordingly, bunker oil whose viscosity is adjusted by mixing the byproduct is inferior to bunker oil from which gasoline is not extracted in terms of ignitability and combustibility.
In this manner, there is a case where bunker oils completely differ from each other in terms of ignitability and combustibility although these oils have the substantially same viscosity. Accordingly, it is difficult to perform the inspection of quality of bunker oil based on viscosity, specific gravity or the like. Bunker oil is fuel so that, originally, quality of bunker oil such as ignitability and combustibility should be evaluated by analyzing components of bunker oil. However, bunker oil which contains residue oil at a high rate has an extremely large number of carbon atoms and hence, under a current situation, the analysis of components of bunker oil is technically difficult. Accordingly, the current circumstance is that quality of bunker oil cannot be inspected unless bunker oil is actually burnt.
As a method for inspecting quality of fuel by actually burning fuel, there have been mainly known a method where quality is determined based on a rate of heat generation by combustion of fuel, and a method where quality is determined based on a combustion state of fuel by observing a flame generated along with combustion of fuel.
In the former method, that is, in the method which determines quality of fuel based on a rate of heat generation based on combustion of fuel, a change in pressure in a combustion chamber where fuel is burnt is thermodynamically analyzed, a rate of heat generation is calculated based on combustion of fuel, a combustion state of fuel is estimated based on the calculated rate of heat generation. However, it is difficult to accurately determine quality of fuel by estimating a combustion state of fuel based on a change in pressure in the combustion chamber.
On the other hand, in the latter method, that is, in the method which determines quality based on a combustion state of fuel, quality of fuel is evaluated by directly observing a combustion state (flame) of fuel in a combustion chamber by a camera or the like through an observation window. As such a method where quality is determined based on a combustion state of fuel, there have been known techniques disclosed in JP-A-2001-329906 (patent document 1) and Japanese Patent 4105742 (patent document 2), for example.
The technique disclosed in patent document 1 is a technique where a length of a flame when fuel is injected and is burnt or a post combustion time where fuel is burnt in a succeeding manner after fuel injection is finished is used as an index, and data on good fuel which is obtained by measurement in advance and data on fuel which is an object to be inspected are compared to each other so as to determine goodness or badness of combustibility of fuel. Further, the technique disclosed in patent document 2 is a technique where ignition delay (time from injection of fuel to ignition) and a change in quantity of light immediately after starting combustion are used as indices, and grading of fuel or determination of fuel quality is performed using such indices.
However, the technique disclosed in patent document 1 has a drawback that it is difficult for a camera for observing a combustion state of fuel to acquire sufficient time resolution for determining quality of fuel in view of a cost or the like. Further, the number of data for determining quality of fuel is not sufficient. Further, conventional quality determinations including the determinations disclosed in patent document 1 and patent document 2 are not performed based on data of a result obtained by actually using fuel in an engine of a foreign-bound ship or the like. Actually, the result of determination based on the conventional quality determination is not sufficient in reliability in actually using fuel on which the result of determination is obtained.